The Gimli Glider is the nickname of an Air Canada aircraft which was involved in a notable aviation accident. On 23 July 1983, Air Canada Flight 143 , a Boeing 767-200 jet, ran completely out of fuel at 41,000 feet (12,500 m) altitude, about halfway through its flight from Montreal to Edmonton via Ottawa. The crew was able to glide the aircraft safely to an emergency landing at Gimli Industrial Park Airport, a former airbase at Gimli, Manitoba.
The subsequent investigation revealed corporate failures and a chain of minor human errors which combined to defeat built-in safeguards. In addition, fuel loading was miscalculated through misunderstanding of the recently adopted metric system which replaced the Imperial system.
History
On 22 July 1983, the day before the incident, Air Canada's Boeing 767 (registration C-GAUN, c/n 22520/47) flew from Toronto to Edmonton where it underwent routine checks. The next day it was flown to Montreal. Following a crew change, it departed Montreal as Flight 143 for the return trip to Edmonton via Ottawa, with Captain Robert (Bob) Pearson and First Officer Maurice Quintal at the controls.
Running out of fuel
At 41,000 feet (12,000 m), over Red Lake, Ontario, the aircraft's cockpit warning system sounded, indicating a fuel pressure problem on the aircraft's left side. Assuming that a fuel pump had failed, the pilots turned it off, as gravity would still feed fuel to the aircraft's two engines. The aircraft's computer indicated that there was still sufficient fuel for the flight, but, as the pilots subsequently realized, the calculation was based on incorrect settings. A few moments later, a second fuel pressure alarm sounded, prompting the pilots to divert to Winnipeg. Within seconds, the left engine failed and they began preparing for a single-engine landing.
As they communicated their intentions to controllers in Winnipeg and tried to restart the left engine, the cockpit warning system sounded again, this time with a long "bong" that no one present could recall having heard before. This was the "all engines out" sound, an event that had never been simulated during training. Seconds later, most of the instrument panels in the cockpit went blank as the right-side engine also stopped and the 767 lost all power.
The 767 was one of the first airliners to include an Electronic Flight Instrument System (EFIS), a system that required the electricity generated by the aircraft's jet engines in order to operate. With both engines stopped, the system went dead, leaving only a few basic battery-powered emergency flight instruments. While these provided basic but sufficient information with which to land the aircraft, a vertical speed indicator – which would indicate the rate at which the aircraft was sinking and therefore how far it could glide unpowered – was not among them.
In airliners the size of the 767, the engines also supply power for the hydraulic systems without which the aircraft cannot be controlled. Such aircraft are therefore required to accommodate this kind of power failure. As with the 767, this is usually achieved through the automated deployment of a ram air turbine, a generator driven by a small propeller, which in turn is driven by the forward motion of the aircraft. As the Gimli pilots were to experience on their landing approach, a decrease in this forward motion means a decrease in the power available to control the aircraft.
Landing at Gimli
In line with their planned diversion to Winnipeg, the pilots were already descending through 28,000 feet (8,500 m) when the second engine shut down. They immediately searched their emergency checklist for the section on flying the aircraft with both engines out, only to find that no such section existed. Captain Pearson, however, was an experienced glider pilot, which gave him familiarity with some flying techniques almost never used by commercial pilots. In order to have the maximum range and therefore the largest choice of possible landing site, he needed to fly the 767 at a speed known as the "best glide ratio speed". Making his best guess as to this speed for the 767, he flew the aircraft at 220 knots (410 km/h; 250 mph). First Officer Maurice Quintal began making calculations to see if they could reach Winnipeg. He used the altitude from one of the mechanical backup instruments, while the distance traveled was supplied by the air traffic controllers in Winnipeg, measuring the distance the aircraft's echo moved on their radar screens. The aircraft had lost 5,000 feet (1,500 m) in 10 nautical miles (19 km; 12 mi), giving a glide ratio of approximately 12:1. The controllers and Quintal both calculated that Flight 143 would not make it to Winnipeg.
At this point, Quintal proposed his former airforce base at Gimli as a landing site. Unknown to him, however, one of the two parallel, equal length runways was now used as a dragstrip. The other runway was used regularly and maintained to a serviceable condition year round. As a result of the runway's conversion to use as a dragstrip, the runway now had two racing lanes separated by a guard rail running down the middle of it. Furthermore, a "Family Day" was underway at the dragstrip that day and the area around the decommissioned runway was full of cars and campers. The decommissioned runway itself was being used to stage a race.
Without power, the pilots had to try lowering the aircraft's main landing gear via a gravity drop, but, due to the airflow, the nose wheel failed to lock into position. The decreasing forward motion of the aircraft also reduced the effectiveness of the Ram Air Turbine (RAT), making the aircraft increasingly difficult to control because of the reduced power being generated. As the runway drew nearer, it became apparent that the aircraft was too high and fast. They ran the risk of running out of runway before the aircraft stopped. The lack of hydraulic pressure prevented flap/slat extension. These devices are used under normal landing conditions to reduce the speed of the aircraft for a safe landing. They briefly considered executing a 360 degree turn but came to the conclusion they did not have enough altitude for the maneuver. Pearson decided to execute a forward slip to increase drag and lose altitude. This maneuver is commonly used with gliders and light aircraft to descend more quickly. At the time Pearson executed the slip, the aircraft was flying over a golf course, and one passenger reportedly said "Christ, I can almost see what clubs they're using!".
As soon as the wheels touched the runway, Pearson "stood on the brakes", blowing out two of the aircraft's tires. The unlocked nose wheel collapsed and was forced back into its well, causing the aircraft's nose to scrape along the ground. The plane slammed into a guard rail which helped slow it down.
None of the 61 passengers was seriously hurt during the landing. A minor fire in the nose area was soon put out by racers and course workers armed with fire extinguishers. As the aircraft's nose had collapsed onto the ground, its tail was elevated and there were some minor injuries when passengers exited the aircraft via the rear slides. These were treated by a doctor who had been about to take off in an aircraft on Gimli's remaining runway.
Investigation
An Air Canada investigation concluded that the pilots and mechanics were at fault. It was also subsequently investigated by the predecessor of the modern Transportation Safety Board of Canada; while concluding that Air Canada management was responsible for "corporate and equipment deficiencies", the report praised the flight and cabin crews for their "professionalism and skill". It noted that Air Canada "... neglected to assign clearly and specifically the responsibility for calculating the fuel load in an abnormal situation", finding that the airline had failed to reallocate the task of checking fuel load that had been the responsibility of the flight engineer on older (three-crew) aircraft.
Fuel Quantity Indicator System
Information about the amount of fuel in the tanks of a Boeing 767 is computed by the Fuel Quantity Indicator System (FQIS) and displayed on gauges in the cockpit. The FQIS on the incident aircraft was a dual processor channel, each calculating the fuel independently and cross-checking with the other. In the event of one failing the other could still operate alone, but under these circumstances the indicated quantity was required to be cross-checked against a floatstick measurement before departure. In the event of both channels failing there would be no fuel display in the cockpit, and the aircraft would be considered unserviceable and not authorized to fly.
After inconsistencies were found with the FQIS in other 767s, Boeing issued a service bulletin for the routine checking of this system. An engineer in Edmonton duly did so when the aircraft arrived from Toronto following a trouble-free flight the day before the incident. It was whilst conducting this check that the FQIS failed completely and the cockpit fuel gauges went blank. The engineer had previously encountered the same problem earlier in the month when the same aircraft had arrived, again from Toronto, with an FQIS fault. He found then that disabling the second channel by pulli
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